What instruction should be given to a patient preparing to wear a Holter monitor?

When preparing to wear a Holter monitor, it is essential to inform the patient to depress the event marker when they experience significant symptoms. This action allows the healthcare provider to correlate symptoms with the EKG data recorded by the monitor, which assists in identifying any arrhythmias or cardiac events that occur during the monitoring period. The event marker helps in pinpointing specific moments that may require further evaluation, making it a crucial instruction for the patient's understanding and active participation in their cardiac health monitoring.

The other choices may not be appropriate or necessary in this context. For instance, limiting all physical activity could lead to unrepresentative results, as normal daily activities can provide important information about the heart's function. Keeping a diary of meals is generally not a specific requirement related to Holter monitoring, though it can be beneficial for broader dietary and health assessments. Advising the patient to avoid all medications without professional guidance could lead to unintended health consequences, as some medications may be essential for their condition during monitoring.